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-   -   Improve gas mileage on a 427 so ? (http://www.clubcobra.com/forums/all-cobra-talk/143284-improve-gas-mileage-427-so.html)

Etype66 02-25-2020 12:09 AM
Hi Guys
Thanks to all for your return
After reading all your messages, I think a good advice is to change the Top loader for a 5 speed box and put the top loader on a shelf. I will try also a vacuum advance distributor.
Will let you know the difference. It may help as I'm not the only one to think about gas mileage no ? Take care !

MKS427 02-25-2020 06:26 AM
Eric,
The gearing is different from trans to trans, so you will want to evaluate the rear gears too, or you will top out in first quick.

Assuming 26.5" tires
Toploader 2.32 1.69 1.29 1 3.55 or 3.73
TKO-500 3.27 1.98 1.34 1 0.68 ~ 3.08
TKO-600 2.87 1.89 1.28 1 0.82 0.64 ~ 3.27

Good luck.

t walgamuth 02-25-2020 06:32 AM
Changing the gear ratio is the most cost effective way to increase fuel economy assuming your car is in good tune.....either the rear end or with an od trans if you don't already have.

lnfletcher 02-25-2020 06:53 AM
I run the TKO600 with the 0.64 OD with 3.50 gears, cruises 70 at about 1900 and my 427w gets about 15 on the interstate. The torque of the 427 works great with this combo. IMO.

ACHiPo 02-25-2020 08:01 AM
Quote:
Originally Posted by MKS427 (Post 1472318)
Eric,
The gearing is different from trans to trans, so you will want to evaluate the rear gears too, or you will top out in first quick.

Assuming 26.5" tires
Toploader 2.32 1.69 1.29 1 3.55 or 3.73
TKO-500 3.27 1.98 1.34 1 0.68 ~ 3.08
TKO-600 2.87 1.89 1.28 1 0.82 0.64 ~ 3.27

Good luck.
The TKO-500 comes in two OD gearings, one at 0.68 and another at 0.82. The lower ratio will help your mileage more IF your differential and engine torque curve work well at cruising speed. I went with 0.82 on my new FE-powered car and love it--crappy mileage, but a great OD gearing with my 3.31 rear end and 27" tires. I have 0.68 on my SBF-powered car and mileage is definitely better, but I need to be cruising at 75 or above for the motor to be in the power band. Of course that could be helped with a different cam and intake. Lots of roads to Rome...

tomshep 02-25-2020 11:02 PM
Quote:
Originally Posted by MKS427 (Post 1472318)
Eric,
The gearing is different from trans to trans, so you will want to evaluate the rear gears too, or you will top out in first quick.

Assuming 26.5" tires
Toploader 2.32 1.69 1.29 1 3.55 or 3.73
TKO-500 3.27 1.98 1.34 1 0.68 ~ 3.08
TKO-600 2.87 1.89 1.28 1 0.82 0.64 ~ 3.27

Good luck.
For clarification, the TKO 600 doesn't have two overdrives. You choose between the .82 or .64.

Tom

Gaz64 02-25-2020 11:23 PM
Quote:
Originally Posted by tomshep (Post 1472385)
For clarification, the TKO 600 doesn't have two overdrives. You choose between the .82 or .64.

Tom
Yes, that's correct, both are 5 speed boxes TKO-500 for 500 lbft, TKO-600 for 600 lbft.

patrickt 02-26-2020 06:36 AM
Quote:
Originally Posted by lnfletcher (Post 1472322)
I run the TKO600 with the 0.64 OD with 3.50 gears, cruises 70 at about 1900 and my 427w gets about 15 on the interstate. The torque of the 427 works great with this combo. IMO.
In contrast, I have the TKO with the 0.64OD and, with my FE stroked and bored to 447 cubic inches, solid flat tappet cam with 245/245 degrees at .050 and 96 degrees of overlap, a Holley 750 vac secondary, when I have her tuned to absolute perfection I get 10.5 mpg around town and a little highway, with no aggressive acceleration, and maybe 13 mpg on the highway alone -- and that's with the secondaries never opening. And when I say tuned to perfection, I mean tuned to perfection.:cool: The only way I could ever get 15mpg is if I was driving down hill off a mountain.

olddog 02-26-2020 08:42 AM
Patrickt - are you running vacuum advance? If so, ported or manifold?

Tuned to perfection would indicate yes you are, but......

bwcobra15 02-26-2020 08:59 AM
I have 427W with quick fuel 780 carb, TKO600 w/.82 OD, 3.50:1 diff, 15" tires ... and I get 11 mpg AT BEST when cruising on the highway. I'm thinking i'm running about 2700 rpm at 75 mph.

I would have gone with the Tremec Magnum 6-speed with two ODs but the magnum is 3.5" inches longer and my driveshaft would be the size of a Dr Pepper can

I'm thinking of going to 3.27:1 differential .... I have 600+ ft lbs of torque that could pull it I think .


.

patrickt 02-26-2020 09:08 AM
Quote:
Originally Posted by olddog (Post 1472398)
Patrickt - are you running vacuum advance? If so, ported or manifold?

Tuned to perfection would indicate yes you are, but......
No, my MSD billet distributor has no vacuum advance -- it's all mechanical. That said, here is my curve. All in at 35 degrees, one light blue and one light silver spring.

http://www.clubcobra.com/photopost/d...dium/curve.jpg

olddog 02-26-2020 10:06 AM
So it is has never been perfectly tuned. Now you may have had the engine, as it exists, tuned to its best possible state.

Your engine, when cruising down the road, at a very light load between 1500-2000 rpms, would make its maximum brake torque (MBT) somewhere between 40-50 degrees advance. If you were to tune it to the correct advance, at these conditions, the car would accelerate or you would have to back off of the throttle to maintain the same speed. This would result in better fuel mileage.

If you want to prove this, fill your tank, start your engine. Set the initial timing to 20 Deg. Now do not step hard on the throttle, as you have way too much timing for a medium load, let alone a hard load. Now take it for a light cruise for about 50 miles. Return the timing to 10 Deg before you shut it off, then fill the tank, and calculate your MPG.

PS
The idle will likely go up quit a bit. Just for this quick test I wouldn't bother turning it down, but it might be safer to do so. Count the turns to make it easier to put back, if you do. This fact also proves that increasing the timing is increasing MBT at this extremely lite load.

undy 02-26-2020 11:03 AM
Just my thoughts...

1) If you're worried about fuel mileage then you're driving/own the wrong car.

2) You should be worried if it isn't hitting on all 8 and the HP is too low.

I'll somewhat apologize for my apparent candidness.

patrickt 02-26-2020 11:57 AM
Quote:
Originally Posted by olddog (Post 1472405)
So it is has never been perfectly tuned. Now you may have had the engine, as it exists, tuned to its best possible state.
No argument there, but I spec'd my engine to be quite similar to the 1963ish engines -- for good and for bad. My cam is, arguably, 50 years behind the curve and, of course, no vacuum advance is exactly like it sounds, no advance. My carb is another item that is pretty much the same as Ford would slap on 50+ years ago. C'mon, who puts in a SFT cam nowadays? Especially one that was spec'd decades ago? But the sound, smell, and feel of it simply can't be beat -- even if I left 50 horses and 5 mpg on the table (maybe more?). And she is tuned to her own level of perfection -- she is as "perfect" as perfect can get when you are talking basically old-style stuff. No EFI, no hydraulic cam, no roller cam, no triple circuit carb, none of that. OK, she does have a MSD, and that was my nod to the 21st century -- but you can't see it unless you look up over the passenger's feet.:LOL:

olddog 02-28-2020 08:43 AM
Patrickt

I get your nostalgia driven desire to do what you did, and that is fine. Different strokes for different folks is part of the fun for me, when I go to the London Ohio Cobra show. There is such a diversity of ideas in the builds. I can imagine how boring it would be, if every car there was identical except for the color of the paint.

However, on the other hand, now I am curious if the original street Cobra with a 428 had vacuum advance. I would guess it did. The 427 race version maybe yes, maybe no. I honestly have no clue.

Personally for a car driven on the street, I feel it should have vacuum advance. Why needlessly burn up a natural resource and pollute the atmosphere for no good reason? Well other than your too lazy to learn how to properly tune the darn thing after putting radical cam in that dropped the manifold vacuum in half. It is a considerable amount of work.

patrickt 02-28-2020 08:55 AM
Quote:
Originally Posted by olddog (Post 1472528)
However, on the other hand, now I am curious if the original street Cobra with a 428 had vacuum advance. I would guess it did. The 427 race version maybe yes, maybe no. I honestly have no clue.
Nor do I. My build is closer to the 427 flavor, with a SCAT stroker at 4.125" and a slight bore out. Light Wiseco pistons, light aluminum roller rockers, aluminum flywheel, balancer, SFT cam, it's all designed to rev quickly and easily. At a standstill, I wouldn't say she actually revs when you tap the gas, rather she explodes. Seriously. But, nowadays, I bet I can go an entire summer and only open the secondaries once or twice, maybe not even that.

olddog 02-28-2020 09:12 AM
Throttle response would better with Vacuum Advance. However the old vacuum advance physically has to move and vacuum has to drop with a fair amount of area to bleed off, so it cannot drop down to the mechanical advance only point, as quickly as needed like EFI can do. If you are driving along in a higher gear and stomp it, the engine will typically get about two pings in. In the lower gears, you would blow the tires off the wheels.

patrickt 02-28-2020 09:17 AM
Quote:
Originally Posted by olddog (Post 1472531)
Throttle response would better with Vacuum Advance. However the old vacuum advance physically has to move and vacuum has to drop with a fair amount of area to bleed off, so it cannot drop down to the mechanical advance only point, as quickly as needed like EFI can do. If you are driving along in a higher gear and stomp it, the engine will typically get about two pings in. In the lower gears, you would blow the tires off the wheels.
The rubber on my tires are as old and hard as a fifty year old pencil eraser -- they are way overdue for a change. In lower gears, they break loose with about 30% throttle.

Gaz64 02-28-2020 05:55 PM
Quote:
Originally Posted by patrickt (Post 1472532)
The rubber on my tires are as old and hard as a fifty year old pencil eraser -- they are way overdue for a change. In lower gears, they break loose with about 30% throttle.
Geez Pat, you need some more grip.

You have a form of traction control, limiting throttle opening.

patrickt 02-28-2020 06:14 PM
Quote:
Originally Posted by Gaz64 (Post 1472568)
Geez Pat, you need some more grip.

You have a form of traction control, limiting throttle opening.
No question about it. New shoes are on the to-do list for this season. I said that last season though, but somehow never got around to it.%/


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